This invention relates to a compact apparatus for treating waste water with activated sludge coated on a carrier, and more particularly to a unit type treating apparatus that can be connected in series or parallel when increasing the capacity of the apparatus.
A method of treating waste water with activated sludge has been used widely and in such method and apparatus, attempts have been made to increase BOD (biological oxgyen demand) volume load. Thus, it has been proposed to deposit activated sludge on a carrier made up of particles of activated carbon, coke, calcium carbonate, etc. for the purpose of improving the efficiency of treating waste water. However, when the carrier particles are not satisfactorily coated with the activated sludge due to the flow of the particles in an aeration tank, the activated sludge peels off the particles, thus degrading the efficiency.
We have already invented an improved method and apparatus in which particles of coral are used as the carrier and have filed a Japanese patent application No. 154882/1981.
Although this method can efficiently purify contaminated waste water by coral particles acting as a carrier and coated with activated sludge, the loss of the carrier particles is large. In other words, when discharging purified water together with sludge peeled off from the carrier particles to the outside of a treating tank, a considerable quantity of the carrier particles is also discharged. Furthermore, as the treating tank was cylindrical, a large floor space was necessary where a number of treating tanks are juxtaposed for the purpose of increasing overall treating capacity. In addition, a considerable amount of the carrier particles tends to accumulate or precipitate on the bottom of the treating tank while the carrier particles are circulated through the tank together with the waste water. As a susbstantial quantity of the carrier particles accumulates, anaerobic bacteria grows, thereby promoting digestion.